This invention relates to a process for genetic alteration of mammalian cell lines and animals such that they express the protein encoded by the human Islet Amyloid Polypeptide (IAPP) gene. IAPP, formerly known as amylin, is the major protein component of pancreatic islet amyloid that forms in the pancreata of Non-insulin Dependent Diabetes Mellitus (NIDDM) patients. Recent studies of IAPP structural and functional characteristics suggest that IAPP, along with insulin and other hormones, plays a major role in carbohydrate metabolism. IAPP is produced, stored and secreted by pancreatic .beta. cells in the islets of Langerhans. It can mimic the phenomenon of insulin resistance seen in NIDDM by inhibiting glucose uptake and glycogen synthesis in muscle, and liver tissue. The generation of amyloid deposits in humans is thought to be due to the ability of the center portion of the peptide (amino acids 20-29) to form a .beta. pleated sheet structure, Rodent IAPP differs from human IAPP in that the sequences in this otherwise highly conserved protein between amino acids 20-29 are not conserved and amyloid deposits do not form in rodent pancreata. A working hypothesis is that overexpression of human IAPP leads to insulin resistance in peripheral tissues and in the formation of amyloid deposits.
Transgenic animals, especially mice, have proven to be very useful in dissecting complex systems to generate new information about human disease. Selective expression of human genes in such mice has generated novel model systems to study disease, especially when overexpression of a gene results in a disease state. With such transgenic mice, one can address issues concerning (1) tissue specificity of expression; (2) testing of hypotheses that overexpression of a particular gene leads to disease; (3) the number and identity of tissues/organs that are affected by this overexpression; and (4) effects of various treatments, including drugs, on the progression or amelioration of the disease phenotype.
The generation of transgenic mice that express human IAPP has been reported in the literature, though none of these animals developed a diabetic phenotype. Niles Fox et al. (FEBS Letters 323, 40-44 [1993]) constructed a transgene that fused the rat insulin promoter sequence to a genomic DNA fragment containing the entire human IAPP gene (exons 1-3 and introns 1 and 2). Transgene RNA expression was detected in pancreas, anterior pituitary and brain. Although plasma IAPP levels were 5-fold elevated relative to nontransgenic littermates, no metabolic consequence of this elevation was observed. C. B. Verchere et al. (Diabetologia 37, 725-729 [1994]) used a 600 bp fragment encoding the entire human proIAPP sequence. Their transgenic animals exhibited greater pancreatic content of both IAPP and insulin relative to nontransgenic littermate controls. Increased secretion of both hormones was also detected in perfused pancreas studies. No clinical manifestations of this enhanced storage and secretion were observed. Hoppener et. al. (Diabetologia 36, 1258-1265 [1993]) described the generation of multiple transgenic lines that expressed either human or rat IAPP in the mouse endocrine pancreas. Hoppener's group used a 703 bp rat insulin II promoter fragment to drive expression of human or rat IAPP from genomic DNA fragments. Plasma IAPP levels were up to 15 fold elevated but no hyperglycemia nor hyperinsulinemia were observed. In a subsequent study, no amyloid plaque was seen to accumulate in vivo but intra- and extracellular amyliod fibrils did form when islets from these transgenics were cultured in vitro under conditions mimicking hyperglycemia (De Koning et al. Proc. Natl. Acad. Sci. 91, 8467-8471 [1994]).